Bestatin [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-(S)-leucine] is a known compound having the formula ##STR1## It exhibits an enhancement of immune response such as delayed-type hypersensitivity, and activates the defensive mechanism of a living body thereby showing a carcinostatic effect. Thus, it has a promising utility as a pharmaceutical.
(A) U.S. Pat. No. 4,052,449 discloses bestatin and a process for its preparation by fermentation of Streptomyces olivoreticuli ATCC No. 31159. U.S. Pat. No. 4,029,547 has a substantially identical disclosure.
(B) U.S. Pat. No. 4,189,604 discloses a synthetic procedure for preparing bestatin. U.S. Pat. No. 4,240,975 has a substantially identical disclosure.
(C) U.S. Pat. No. 4,281,180 discloses another synthetic procedure for the preparation of bestatin.